When Tina Celes came back from the incursion she took part along with Uriel in the cathedral, the first thing she did was to inform her father about the existence of the underground structures called dungeons. She didn't know much about them, only what Uriel told them, but just the possibility of controlling an orichalcum vein was enough to pique Piero's interest.
He was a pragmatic man who didn't reach his position by luck, someone like him would never trust his daughter's words at face value no matter how much he loved her. Nevertheless, when the Mapple corporation got involved he knew there was money to be made in the Lost city and as one of the most important figures in the whole city he felt entitled to whatever riches could be acquired in its vicinity.
Needless to say, this included getting a share of the profit from the alleged dungeon beneath the Alamo, but things weren't so easy.
